Patent GB-1170067-A (GB)
Title: Accelerometer
Inventor: JACOBS EARL DONALD
IPC: G01P15/18
Filed: 1966-10-24
Abstract: 1,170,067. Lasers. NORTH AMERICAN AVIATION Inc. 24 Oct., 1966, No. 47624/66. Heading H1C. An accelerator comprises a gas laser structure having an acceleration sensor located between or forming part of the resonator mirrors, the sensor in operation causing an effective change in the optical length of the resonator and thereby changing the output frequency. A threeaxis accelerometer is shown in Fig. 2 in which four gas active media 15 are located between a fully reflecting mirror 14 and a partially transmitting mirror 13, three of the media having each a respective acoelerometer stress sensor 11, 10, 16 one for each axis in its emission path, and the remaining active medium being associated with a reference sensor 12 unaffected by acceleration. Internal mirrors 21 are necessarily associated with sensor 16 and its associated active medium. Externally to the laser fully reflecting mirrors 17 and partially reflecting mirrors 18 direct each sensor-influenced output to a respective axis detector 19, 20, 22 together with a reference output from the fourth active medium, acceleration being detected in both magnitude and direction as a frequency difference. Helium-neon gas is used as the active medium. The accelerometer may be made as a composite block formed by fitting together two identical quartz housings 30, Fig. 3a (not shown) and Fig. 3b, the resonator mirorrs 13, 14 and internal mirrors 21 being applied to the housings at 31, 37 and M1-M4, and the cavities 32 and 34, 35, 36 being filled with gaseous active medium and acceleration sensors respectively. Gas discharge in the active medium cavities may be established by passing D.C. through the gas using electrodes inserted in the block, or by inductively coupling A.C. or R.F. through electrodes outside the block. A basic accelerometer is shown in Fig. 4 in which a polarization isolator 43 resolves the beam emitted by active medium 42 into two beams of different polarization, the beams passing respectively through a stress sensor material 44 and an unstressed reference material 45. Outside the resonator defined by mirrors 41, 46, the two beams are combined in a polarization combiner 47 and the difference frequency between the two beams detected by a heterodyning apparatus 48. A similar arrangement, Fig. 5, separates the generated beam into ordinary and extraordinary rays O, E by using a double refracting material 50, the beams being recombined by externally-located double refracting material 51 after passing through the stress and reference sensors 55, 56 respectively. After passing through an analyser 52, the frequency difference in the output is detected by heterodying. In a modification. Fig. 6 (not shown), the double refracting material internal of the resonator is stress sensitive and is mass-loaded so as to act as a sensor determining the frequency of the ordinary and extraordinary rays passed. A further arrangement, Fig. 7, uses two active media 15 to produce a signal beam and a reference beam. Each active medium has its own resonator formed by mirrors 14, 70 and 14, 71, the reflecting surface of mirror 71 being deformable under acceleration. A push-pull form of output is obtained in Fig. 8 (not shown) in which two beams from separate active media pass through opposite ends of a common acceleration stress sensor.